Scanning electron microscopy (SEM) cathodoluminescence (CL) experiments were used to determine the existence and direction of piezoelectric fields in a commercial InGaN multiple-quantum-well (MQW) light-emitting diode (LED). The CL emission peak showed a blueshift with increasing reverse bias due to the cancellation of the piezoelectric field. A full compensation of the piezoelectric field was observed followed by a redshift with a further increase of reverse bias, indicating that flat-band conditions had been reached. We determined the piezoelectric field points in the [000-1] direction and estimated the magnitude to be approximately 1 MV/cm. SEM-CL carrier generation density variation and electroluminescence experiments were also used to confirm the existence of a piezoelectric field in the InGaN MQW LED.